title: Sex and vasodilator responses to hypoxia at rest and during exercise.
abstract: In humans, β-adrenergic receptor activation causes a substantial portion of hypoxic vasodilation in skeletal muscle at rest and during forearm exercise. Recent evidence suggests that β-adrenergic receptors are either more sensitive or upregulated in young women vs. men. Therefore, we examined whether sex influences hypoxic vasodilation in 31 young subjects (15 women/16 men; 26 ± 1 yr). We also examined whether potential sex-related differences existed in a group of older adults (6 women/5 men; 61 ± 2 yr). All subjects performed forearm exercise at 10 and 20% of maximum under normoxic and hypoxic [80% arterial O2 saturation (So2)] conditions. Forearm vascular conductance (FVC; ml · min(-1) · 100 mmHg(-1)) was calculated from blood flow (ml/min) and blood pressure (mmHg). At rest, young women demonstrated a greater vasodilator response to hypoxia compared with men (39 ± 12 vs. 13 ± 6%, P < 0.05). The absolute compensatory vasodilator response (hypoxic FVC-normoxic FVC) during exercise was similar between sexes, but the relative change was greater in young women at 10% (28 ± 5 vs. 17 ± 3%, P < 0.05) and 20% exercise (29 ± 4% vs. 15 ± 3%, P < 0.01). Additionally, the absolute changes in vasodilation after normalizing the response to forearm volume or workload were greater in young women during exercise (P < 0.05). Interestingly, the compensatory vasodilator responses between older women and men were similar at 10 and 20% exercise, regardless of whether the response is expressed as absolute, relative, or absolute change normalized for forearm volume or workload (P = 0.054-0.97). Our data suggest that the compensatory vasodilator response to hypoxic exercise is greater in young women compared with men. However, sex-specific differences appear to be lost with aging.
authors.affiliation: Department of Physical Therapy and Rehabilitation Science, Carver College of Medicine, University of Iowa, Iowa City, Iowa.
authors.forename: Darren P
authors.initials: DP
authors.lastname: Casey
authors.forename: John R A
authors.initials: JR
authors.lastname: Shepherd
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000367:Age Factors; D015415:Biomarkers / Q000097:blood; D001783:Blood Flow Velocity; D001794:Blood Pressure; D004837:Epinephrine / Q000097:blood; D015444:Exercise; D005260:Female; D005542:Forearm; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000098:blood supply*; D009638:Norepinephrine / Q000097:blood; D012039:Regional Blood Flow; D012119:Respiration; D012189:Retrospective Studies; D012737:Sex Factors; D014664:Vasodilation
chemical_list: D015415:Biomarkers; D009638:Norepinephrine; D004837:Epinephrine
keywords: exercise; hypoxia; sex; vasodilation